Transmission and receiver apparatus and methods

ABSTRACT

The present invention relates to an apparatus and a corresponding method for mapping error correction code encoded time-domain data of at least two mapping input data streams (S 1,  S 2,  . . . , Sn) onto a time-domain mapping output data stream (Q) having a frame structure, comprising a data input ( 102 ) for receiving said at least two mapping input data streams (S 1,  S 2,  . . . , Sn) each being segmented into data blocks (D 1,  D 2,  . . . , DN) carrying error correction code encoded data, a data mapper ( 104 ) for mapping the data blocks (D 1,  D 2,  . . . , DN) of said at least two mapping input data streams (S 1,  S 2,  . . . , Sn) onto frames of said mapping output data stream (Q), each frame comprising a number of frame intervals (F 1,  F 2,  . . . , FM), wherein the data mapper ( 104 ) is adapted for mapping the data blocks (D 1,  D 2,  . . . , DN) onto said frame intervals such that each frame interval (F 1,  F 2,  . . . , FM) carries sequentially arranged data blocks (D 1,  D 2,  . . . , DN) from various mapping input data streams (S 1,  S 2,  . . . , Sn) and that within a frame the mapping of data blocks (D 1,  D 2,  . . . , DN) from the various mapping input data streams (S 1,  S 2,  . . . , Sn) onto frame intervals (F 1,  F 2,  . . . , FM) is different from frame interval to frame interval, and a data output ( 110 ) for outputting said mapping output data stream (Q).

FIELD OF INVENTION

The present invention relates to an apparatus for mapping errorcorrection code encoded time-domain data of at least two mapping inputdata streams onto a time-domain mapping output data stream having aframe structure. The present invention also relates to a transmissionapparatus for transmitting data within a data transmission system.Further, the present invention relates to corresponding methods as wellas a computer program for implementing said mapping method on acomputer.

The present invention relates, for instance, to the field of DigitalVideo Broadcasting (DVB) utilizing Orthogonal Frequency DivisionMultiplexing (OFDM), in particular to a frame builder used in such datatransmission systems for DVB. But the present invention can also beapplied in other fields like Digital Audio Broadcasting (DAB).

BACKGROUND OF THE INVENTION

In digital communications or data transmission systems it is known toapply time interleaving or subslicing to combat the effects of timeselective fading or the influence of noise bursts. One aspect of timeselective fading is the so-called fast fading, which is caused bymultipath propagation. The signals of the different paths from atransmitter (or from multiple transmitters of, for instance, OFDM SingleFrequency Networks), superimpose each other in amplitude and phase. Asespecially the phase varies over the frequencies, this causes afrequency selective channel. Therefore, the frequencies at the receiver(i.e. related OFDM sub-carriers) have different reception amplitudes.

Additionally, the amplitude and the phase of the different receptionpaths also depend on the position of the receiver. In case of a movingreceiver, especially the phase of the signals of the different receptionpaths changes, which causes a time selective channel. The changes in thetime direction can also have a very regular structure. The change rateof this structure over the time axis is proportional to the relativevelocity of the receiver to the transmitter(s) and the transmissionfrequency of the signal. Also other disturbances, such as impulsivenoise, can have a regular structure, e.g. caused by the line cyclefrequency of the power grid or by bursts from other data transmissionsystems, e.g. a GSM communications system.

Any digital data transmission systems, such as systems in accordancewith the DVB-T2 standard (second generation digital terrestrialtelevision broadcasting systems standard), use a framing structure withtime interleaving and/or sub-slicing that applies a regular structure intime domain. This frame structure is generally built by a frame builder,i.e. an apparatus for mapping error correction code encoded time-domaindata of at least two mapping input data streams onto a time-domainmapping output data stream.

SUMMARY OF INVENTION

It is an object of the present invention to provide an apparatus and acorresponding method for mapping error correction code encodedtime-domain data of at least two mapping input data streams onto atime-domain mapping output data stream having a frame structure whichcan advantageously be applied in transmitters of data transmissionsystems with mobile receivers and which provide a good transmission andreception quality despite possible time selective fading effects.Further, it is an object of the present invention to provide atransmission apparatus for transmitting data within a data transmissionsystem and a corresponding transmission method. Still further, it is anobject of the present invention to provide a computer program forimplementing said mapping method.

According to an aspect of the present invention there is provided anapparatus for mapping error correction code encoded time-domain data ofat least two mapping input data streams onto a time-domain mappingoutput data stream having a frame structure, comprising:

a data input for receiving said at least two mapping input data streamseach being segmented into data blocks carrying error correction codeencoded data,

a data mapper for mapping the data blocks of said at least two mappinginput data streams onto frames of said mapping output data stream, eachframe comprising a number of frame intervals, wherein the data mapper isadapted for mapping the data blocks onto said frame intervals such thateach frame interval carries sequentially arranged data blocks fromvarious mapping input data streams and that within a frame the mappingof data blocks from the various mapping input data streams onto frameintervals is different from frame interval to frame interval, and

a data output for outputting said mapping output data stream.

According to another aspect of the present invention there is provided atransmission apparatus for transmitting data within a data transmissionsystem comprising a mapping apparatus in accordance with the presentinvention as defined above and a transmitter unit for transmitting themapping output data stream.

According to further aspects of the present invention there is provideda corresponding mapping method as well as a corresponding transmissionmethod.

Finally, according to another aspect there is provided a computerprogram comprising program code means for causing a computer to carryout the steps of the mapping method in accordance with the presentinvention, when said computer program is carried out on a computer.

Preferred embodiments of the invention are defined in the dependentclaims. It shall be understood that the claimed apparatus, the claimedmethods and the claimed computer program have similar and/or identicalpreferred embodiments as the claimed mapping apparatus and as defined inthe dependent claims.

It has been recognized according to the present invention that theregular structure that is applied in the time domain in manycommunications or data transmission systems in a step of timeinterleaving and/or subslicing are not optimal or not even suited formobile receivers due to fading effects caused by multipath and/orDoppler frequencies (or, more precisely, frequency shifts). Due to theperiodic structure of multipath or Doppler dependent channel transferfunctions in the time direction, particularly when mobile receivers areused, the temporal distance of fadings (or other disturbances having aregular structure) may match exactly the distance of subslices (alsocalled “bursts”; hereinafter generally referred to as “data blocks”) ofone mapping input data stream. A consequence could then be that thereceiver is not able to correct the data of this mapping input datastream (at all, or at least in part) despite the error correction codedata that are generally included in this mapping input data stream.Particularly for mobile receivers the temporal distance of fadings and,thus, the data blocks for input data streams which suffer from suchfadings cannot be foreseen by the network operator or the transmitter.As the transmitter generally serves a large number of receivers, it is,hence, not adjustable to provide optimal transmission conditions for allreceivers.

To overcome this problem it is thus proposed according to the presentinvention to map the data blocks of the at least two mapping input datastreams according to an irregular structure (rather than according to aregular structure as commonly done in the art) onto the frame intervalsof the frames of the mapping output data stream. In other words, whileconventionally the data blocks are regularly mapped onto the frameintervals of a frame, it is proposed according to the present inventionto do this irregularly so that the temporal distance of fadings does nolonger exactly match the distance of data blocks belonging to the samemapping input data stream. Hence, such fading effects having a regularperiodicity affect data blocks belonging to different mapping input datastreams, and an error correction of the affected data streams at thereceiver generally allows or at least improves restoration of theaffected data streams.

The irregular mapping of the data blocks onto the frame intervals ispreferably applied to frames which are regularly structured, e.g. allhaving the same length, but is also applicable to frames which areirregularly structured, e.g. having different lengths.

According to a preferred embodiment the data mapper is adapted formapping the data blocks onto said frame intervals such that within aframe the sequence of mapping input data streams, from which data blocksare mapped onto a frame interval, and/or the size of the data blocksarranged within a frame interval is different from frame interval toframe interval. Preferably, the mapping is done such that the sequenceof data streams and/or the size of the data blocks arranged within aframe interval is different for all frame intervals of a frame.

Conventionally, as for instance provided for in the DVB-T2 standard, thesequence of the mapping input data streams, from which data blocks aremapped onto a frame interval, is identical for all frame intervals of aframe, and is also identical for all frames. This sequence ispredetermined and fixed, and is also known to the receiver to enable itto correctly de-map a received data stream. Further, conventionally thesize of the data blocks that belong to the same mapping input datastream is fixed for all frame intervals of a frame and, generally, alsofor all frames. This results in a regular mapping structure of the datablocks from the various mapping input data streams onto the frameintervals of frames which is broken according to the present invention.Both the sequence of mapping input data streams and/or the size of thedata blocks arranged within a frame interval can generally be selectedfreely by the data mapper such that no longer such a regular mappingstructure is achieved.

For instance, in an embodiment for each frame interval of a frame thesequence can be changed, and in another embodiment the size of the datablocks can be changed after each frame interval.

According to another preferred embodiment the data mapper is adapted formapping the data blocks onto said frame intervals such that the sequenceof mapping input data streams, from which data blocks are mapped ontothe frame intervals of a frame, and/or the size of the data blocksarranged within a frame interval is identical for all frames. In otherwords, the mapping structure that is applied in the frames is identicalfor all frames which has the advantage that the receiver only needs toknow little data about the mapping structure applied in the transmitter,in particular the data mapper of the transmitter, in order to correctlyde-map a received data stream.

According to another embodiment the data mapper is adapted for mappingthe data blocks onto said frame intervals such that the sequence ofmapping input data streams, from which data blocks are mapped onto theframe intervals of a frame, and/or the size of the data blocks arrangedwithin a frame interval is different from frame to frame, in particularis different for a plurality of subsequent frames or for all frames. Inother words, the mapping structure is not identical for all frames, butis different from frame to frame, in particular is different for aplurality of subsequent frames or even for all frames. This has theadvantage that over the frame boundaries no regular mapping structure ispresent so that also fading effects with a longer duration, i.e. over aplurality of frame boundaries, do not have the above-described negativeeffects.

Preferably, the data mapper is adapted for mapping the data blocks ontosaid frame intervals such that within a frame each frame intervalcomprises at least one data block from each mapping input data stream,in particular exactly one data block from each mapping input datastream. This has the advantage, as is commonly known, that other fadingeffects by which, for instance, data within a complete frame or a coupleof frame intervals are affected, do not prevent the error correction ofthe affected mapping input data streams.

Advantageously, an embedding unit is further provided in the apparatusfor embedding a mapping information into the mapping output data streamcomprising an information about the mapping structure of the mapping ofthe data blocks onto said frame intervals for enabling a correctde-mapping of the mapping output data stream. Generally, it is notnecessarily required to embed such a mapping information into themapping output data stream to inform the receiver, in particular thede-embedding unit of a de-mapping apparatus, about the mapping structureapplied by the mapping apparatus. For instance, a fixed (irregular)mapping structure could be applied by the mapping apparatus which ispredetermined in advance so that the de-mapping apparatus knows withoutany additional information how the received data stream has to bede-mapped. Preferably, however, some mapping information is embedded inthe mapping output data stream as proposed according to this preferredembodiment. In this way, the applied mapping structure can generally beselected freely and can, for instance, be changed on demand, forinstance in response to the respective transmission situation.

For instance, as proposed according to a further embodiment, a mappingrule generator can be provided for generating a mapping rule for use bythe data mapper for mapping the data blocks onto said frame intervalsaccording to said mapping rule. The de-mapper in the receiver thenrequires some information about the generated mapping rule or, at least,some kind of start values for initializing the mapping rule generator ifanother instance of the mapping rule generator is also provided in thereceiver. In such case only those start values for initializing themapping rule generator need to be transported to the de-mapper in thereceiver, preferably as mapping information embedded within the mappingoutput data stream.

As the mapping structure is particularly determined by the sequence ofdata blocks within the frame intervals and/or the size of the datablocks arranged within a frame interval the mapping rule generator ispreferably adapted for generating said mapping rule comprising asequence information for use by the data mapper in determining thesequence of mapping input data streams, from which data blocks aremapped onto a frame interval, and/or a size information for use by thedata mapper in determining the size of the data blocks arranged within aframe interval.

Various implementations exist for said mapping rule generator.Generally, any means can be used by which a random or pseudo randomsequence of values can be generated that are then used to determine theirregular mapping structure. In an embodiment, the mapping rulegenerator comprises a scrambling unit for generating a scrambling factoror a shift register, in particular a linear feedback shift register, forgenerating a shift factor for use as a sequence information by the datamapper in determining the sequence of mapping input data streams, fromwhich data blocks are mapped onto a frame interval. Such a scramblingunit or feedback shift register can be easily implemented by appropriatehardware (in analogous circuitry or digital logic) and/or software.

Preferably, the present invention can be applied in data transmissionsystems for digital video broadcasting, for instance for terrestrialtelevision broadcasting or for broadcasting for handheld terminals(according to the DVB-H, DVB-T2 or the upcoming DVB-NGH standard). Whenapplied in those systems the data input is preferably adapted forreceiving said at least two mapping input data streams representingphysical layer pipes, each physical layer pipe being segmented intosubslices or bursts carrying error correction code encoded data, ascommonly used in those data transmission systems. In this context of DVB“physical layer pipe” is understood to be a physical layer (TDM) channelthat is carried by the specified subslices, which may carry one ormultiple services, and “subslice” is understood to be a group of cellsfrom a single PLP, which before frequency interleaving, are transmittedon active OFDM cells with consecutive addresses over a single RFchannel.

However, the invention can also be applied in other data transmission orcommunications systems, for instance in digital mobile systems like DAB(Digital Audio Broadcasting) or MediaFLO (Media Forward Link Only).

According to further aspects a system and a corresponding method fortransmitting and receiving data are presented according to the presentinvention. Such a system comprises a transmission apparatus as describedabove and a corresponding receiver apparatus, wherein the receiverapparatus comprises a) a receiving unit for receiving a time-domainde-mapping input data stream having a frame structure, and b) anapparatus for de-mapping said time-domain de-mapping input data streamhaving a frame structure into at least two de-mapping output datastreams carrying error correction code encoded time-domain data. Saidapparatus for de-mapping comprises b1) a data input for receiving saidtime-domain de-mapping input data stream having a frame structure offrames, each frame comprising a number of frame intervals, wherein eachframe interval carries sequentially arranged data blocks from variousde-mapping output data streams and wherein within a frame the mapping ofdata blocks from the various de-mapping output data streams onto frameintervals is different from frame interval to frame interval, b2) a datade-mapper for de-mapping the frames of said de-mapping input data streaminto said at least two de-mapping output data streams, wherein fromframe interval to frame interval within a frame the de-mapping of datablocks into said at least two de-mapping output data streams is madedifferently, and b3) a data output for outputting said at least twode-mapping output data streams. The apparatus for de-mapping mayadvantageously be further arranged in embodiments in equivalent manneras described above for the apparatus for mapping.

BRIEF DESCRIPTION OF DRAWINGS

These and other aspects of the present invention will be apparent fromand explained in more detail below with reference to the embodimentsdescribed hereinafter. In the following drawings

FIG. 1 shows a schematic block diagram of an embodiment of atransmission apparatus according to the present invention,

FIG. 2 shows a schematic block diagram of an embodiment of a receiverapparatus,

FIG. 3 shows a schematic block diagram of a frame builder as used in thetransmission apparatus shown in FIG. 1,

FIG. 4 shows a diagram illustrating the DVB-T2 frame structure,

FIG. 5 shows a diagram of a single frame illustrating a regular mappingstructure of data blocks onto the frame intervals of the frame,

FIG. 6 illustrates the effect of temporal fading on a frame includingregularly structured data blocks,

FIG. 7 illustrates a frame including irregularly structured data blocksas proposed in an embodiment of the present invention and the effect oftemporal fading,

FIG. 8 shows a schematic block diagram of a mapping apparatus accordingto the present invention,

FIG. 9 shows a mapping output data stream before and afterpost-processing,

FIG. 10 shows a schematic block diagram of a de-mapping apparatus,

FIG. 11 shows several frames with irregularly structured data blocksaccording to the present invention,

FIG. 12 shows a schematic block diagram of a linear feedback shiftregister for use as mapping rule generator in the mapping apparatusshown in FIG. 8,

FIG. 13 illustrates a frame including irregularly structured data blocksas proposed in another embodiment of the present invention and theeffect of temporal fading,

FIG. 14 shows several frames with irregularly mapped data streamsaccording to a further embodiment of the present invention,

FIG. 15 shows the structure of a transmission frame as used according toDAB, and

FIG. 16 shows several transmission frames with irregularly arrangedsub-channels according to a further embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 provides an example block diagram of a Coded OFDM (COFDM)transmitter 20 which may be used for example to transmit video imagesand audio signals in accordance with the DVB-T2 standard and in whichthe invention can be used. In FIG. 1 a program source 1 generates datato be transmitted by the COFDM transmitter 20. A video coder 2, andaudio coder 4 and a data coder 6 generate video, audio and other data tobe transmitted which are fed to a program multiplexer 10. The output ofthe program multiplexer 10 forms a multiplexed stream with otherinformation required to communicate the video, audio and other data. Themultiplexer 10 provides a stream on a connecting channel 12. There maybe many such multiplexed streams which are fed into different branchesA, B etc. For simplicity, only branch A will be described.

As shown in FIG. 1 a COFDM transmitter 20 obtains the stream at amultiplexer adaptation and energy dispersal block 22. The multiplexeradaptation and energy dispersal block 22 randomises the data and feedsthe appropriate data to a forward error correction encoder 24 whichperforms error correction encoding of the stream. A bit interleaver 26is provided to interleave the encoded data bits which, for the exampleof DVB-T2, is the LDPC/BCH(Low-Density-Parity-Check/Bose-Chaudhuri-Hocquenghem) encoder output.The output from the bit interleaver 26 is fed to a bit intoconstellation mapper 28, which maps groups of bits onto a constellationpoint, which is to be used for conveying the encoded data bits. Theoutputs from the bit into constellation mapper 28 are constellationpoint labels that represent real and imaginary components. Theconstellation point labels represent data symbols formed from two ormore bits depending on the modulation scheme used. These data symbolsare passed through a cell and time interleaver 30 whose effect is tointerleave data symbols resulting from multiple LDPC code words.

The data symbols (a multitude of which correspond to a “data block” asdiscussed above and below with reference to the present invention) arereceived by a frame builder 32, with data symbols produced by branch Betc. in FIG. 1, via other channels 31. The frame builder 32 then formsmany data symbols into sequences to be conveyed on COFDM symbols, wherea COFDM symbol comprises a number of data symbols, each data symbolbeing mapped onto one of the subcarriers. The number of sub-carrierswill depend on the mode of operation of the system, which may include,e.g., one of 1 k, 2 k, 4 k, 8 k, 16 k or 32 k. Thus in one example, thenumber of sub-carriers for the 16 k mode is 12096.

Each frame comprises many such COFDM symbols. The sequence of datasymbols to be carried in each COFDM symbol is then passed to the symbolinterleaver 33. The COFDM symbol is then generated by a COFDM symbolbuilder block 37 which introduces pilot and synchronising signals fedfrom a pilot and embedded signal former 36 into the frequencyinterleaved data symbols. An OFDM modulator 38 then forms the OFDMsymbol in the time domain which is fed to a guard interval insertionprocessor 40 for generating a guard interval between OFDM symbols, andthen to a digital to analogue converter 42 and finally to an RFamplifier within an RF front 44 for broadcast by the COFDM transmitter,e.g. from an antenna 46.

FIG. 2 shows an example block diagram of a COFDM receiver 50 which maybe used for example to receive video images and audio signals from aCOFDM transmitter shown in FIG. 1 in accordance with the DVB-T2standard.

An RF signal received at antenna 52 is fed to a frontend (e.g. a tuner)54 and thereafter converted into a digital signal by an analogue todigital converter 56. The digital stream is then demodulated by an OFDMdemodulator 58, whereafter the stream is provided to a channel equalizer60, a symbol deinterleaver 62 and a frame demapper 64 in which the datasymbols that have been formed into sequences by the frame builder 32 ofthe transmitter are de-mapped. Thereafter, the data are de-interleavedby a cell- and time de-interleaver 66 and a bit de-interleaver 70.Between these units 66 and 70 constellation points are de-mapped ontogroups of bits by a constellation demapper 68. Error correction isperformed by an LDPC/BCH decoder 72. Thereafter follow a BBFRAME(baseband frame) processor 74, a dejitter unit 76 and a Null Packetreinserter 78, from which the transport streams (TS) or generic streamencapsulation (GSE) stream are outputted. More details of the generallayout and the function of such a receiver 50 can, for instance, befound in the DVB-T2 standard (in particular in DVB Document A133,February 2009, “Implementation guidelines for a second generationdigital terrestrial television broadcasting system (DVB-T2)”) whichexplanations are herein incorporated by reference and which shall thusnot be explicitly explained in more detail here.

The mapping apparatus according to the present invention can be used insuch a transmitter and can favourably be implemented in the framebuilder 32. A block diagram of a frame builder 32 as described in theDVB-T2 standard and as used in the transmitter shown in FIG. 1 is shownin FIG. 3. The frame builder 32 comprises a compensation unit 321 and acell mapper 322. The compensation unit 321 receives as input modulatedL1 signalling data and compensates for any frame delay in an inputmodule (in particular the adaption and energy dispersal block 22) andany delay in the time interleaver 30. The cell mapper 322 receives asinput the output from the compensation unit 321 and n+1 physical layerpipes PLP0-PLPn. The cell mapper 322 assembles the modulated cells ofthe PLPs and L1 signalling into arrays of active OFDM cellscorresponding to each of the OFDM symbols which will make up the overallframe structure. The cell mapper 322 operates according to dynamicscheduling information produced by a scheduler (not shown in FIG. 1)which is generally part of the input processing and the configuration ofthe frame structure. The output of the cell mapper 322, e.g. the arraysof active OFDM cells, is then provided to subsequent processing, e.g.frequency interleaving and OFDM generation. The present inventionexplained in detail below is generally implemented in the frame builder32 (FIG. 1), in particular the cell mapper 322 (FIG. 2) and/or thescheduler.

The frame de-mapper 64 of the receiver shown in FIG. 2 must be adaptedaccordingly so that it is able to de-map the received data stream thathas been structured by a mapping apparatus implemented in the framebuilder 32 of the transmitter shown in FIG. 1.

The DVB-T2 frame structure is shown in FIG. 4. At the top level, theframe structure consists of super-frames, which are divided into T2frames, which are further divided into OFDM symbols. The super-frame mayin addition have future extension frames (FEF) enabling carriage offrames defined in future extensions of the standard.

As shown in FIG. 4 the T2-frame comprises one P1 preamble symbol,followed by one or more P2 preamble symbols, followed by a configurablenumber of data symbols. The purpose and the insertion of these preamblesymbols as well as the general formation of the T2-frames and of thesuper-frames are explained in detail in the DVB-T2 standard (inparticular in ETSI EN 302 755 V1.1.1 (2009-09) “Digital VideoBroadcasting (DVB): Frame structure channel coding and modulation for asecond generation digital terrestrial television broadcasting system(DVB-T2)” and in the above cited implementation guidelines for DVB-T2)which explanations are herein incorporated by reference and which shallthus not be explicitly explained in more detail here.

If time interleaving or subslicing is used in transmitters of digitalcommunications or data transmission systems, the data is spread over alonger time period. In case of the OFDM modulated DVB-T2 system data areinterleaved and transmitted in multiple data blocks (multiple datablocks being called a subslice in the DVB-T2 standard; also referred toas burst sometimes). This is illustrated in FIG. 5 showing a diagram ofa single frame, e.g. in accordance with the DVB-T2 standard. At thebeginning of each DVB-T2 frame there is a preamble (preamble symbols P1and P2) that allows for synchronization as well as for extraction of theL1 signalling. The following payload data of one PLP (generally alsoreferred to as “mapping input data stream” herein) can be transmitted inmultiple subslices, each marked by D1 for PLP1, D2 for PLP2, etc.:generally up to DN for PLPN; N being 4 here in this example).

Generally, the frame is subdivided into frame intervals (called“sub-slice intervals” according to the DVB-T2 standard) onto which thedata blocks (“sub-slices”) of the various (here four) mapping input datastreams (“physical layer pipes”) are mapped. According to the standard aregular mapping structure is applied as shown in FIG. 5. Accordingly thesequence of the mapping input data streams, from which data blocks aremapped onto a particular frame interval are mapped, is identical for allframe intervals of the frame. In other words, the sequence D1-D2-D3-D4of data blocks in a frame interval is the same for all frame intervalsof the frame. Further, the length of the data blocks of one particularmapping input data stream (e.g. all D1 data blocks) is always constantin all frame intervals. In the examples shown in FIG. 5, the length ofthe data block is also identical for all mapping input data streams inall frame intervals of the frame, although this is not generallyrequired. According to the DVB-T2 standard, the data blocks of differentmapping input data streams may also have different lengths, e.g. thedata blocks D1 may have a different length than the data blocks D2and/or D3 and/or D4. Generally, also the frames are regularlystructured, i.e. the length of the frames is identical for all frames.

If data of one (or a few) data blocks is (are) lost or disturbed, acorresponding data stream can be recovered by a receiver by means of the(forward) error correction, if the data of the remaining data blocks ofthis data stream are received correctly (in particular with sufficientquality). However, this regular mapping structure may also causeproblems due to the regular structure of the Doppler or time-variantmultipath dependent channel transfer function in time direction asexplained above. This is particularly true for all mobile receivers asthe velocity of the receiver in addition to the transmission frequencymay cause temporal fading as depicted in FIG. 6.

FIG. 6 shows the absolute value of the channel transfer function in caseof temporal fading superposed to one frame of data mapped according to aregular mapping structure as shown in FIG. 4. As can be seen thetemporal distance of fadings matches exactly the distance of data blocks(subslices or bursts) of one particular mapping input data stream (PLP)in particular the data blocks D2 of the second mapping input data stream(PLP2). Thus, all data blocks of this mapping input data stream areaffected, and consequently, the receiver will not be able to correct thedata of this data stream by means of the error correction data includedin this data stream.

As the temporal distance of the fadings is also dependent on thereceiver velocity (and other impulsive noise disturbances), it ispractically impossible for the network operator to place the data blocksinto the frame intervals of the frames in such a way that this negativefading effect practically does not occur at any receiver and any datastream. This negative effect gets particularly important, if theduration of the data blocks (i.e. the burst duration or subsliceduration) is far less than the channel coherence time, i.e. the distancebetween two fades, because there is no interleaving effect within thedata block itself. Further, as mentioned above, in such broadcastingsystems the transmitter can not be adjusted for optimal transmission toall receivers it is serving.

This negative effect is avoided or at least mitigated by breaking theregular mapping structure of the data blocks as proposed according tothe present invention and as depicted in FIG. 7 showing an embodiment ofan irregular mapping structure. According to this embodiment theposition of the data of one mapping input data stream (one PLP) ischanged within one frame interval (subslice interval), i.e. the sequenceof the mapping input data streams from which data blocks aresubsequently arranged within a frame interval is different from frameinterval to frame interval within the frame. As shown in FIG. 6, in thefirst frame interval F1 (out of generally M frame intervals F1, F2, . .. , FM; M being 3 here in this example) the sequence is D1, D2, D3, D4,while in the second frame F2 interval the sequence is D3, D4, D2, D1,while in the third frame F3 interval the sequence is D3, D1, D4, D2.Hence, the regular mapping structure in the time domain, as shown inFIGS. 5 and 6, is broken according to the present invention. Theconsequence is, that not only the data blocks of one mapping input datastream are affected by the fades, but the negative effects of the fadesare equally split over all transmitted mapping input data streams(PLPs). As a consequence, the error correction in the receiver is ableto correct the data completely or to a larger extent/with higherprobability.

Regarding the modifications of the regular mapping structure to obtainsuch an irregular mapping structure various options and embodimentsexist, e.g. regarding the change of the mapping sequence of data blocksonto the frame intervals of the frames. One option is that for allframes the same modifications are applied, i.e. after each frame thesame mapping structure is used again. According to another option, theframe boundaries are not taken into account when applying a certainmapping rule for obtaining such an irregular mapping structure, i.e. theirregular mapping structure is generally not identical for subsequent orall frames.

Further, the same sequence of data blocks is not applied in subsequentframe intervals. Preferably, for each frame interval of a frame adifferent sequence is used. According to still another option thesequences are preferably selected such that data blocks from the samemapping input data stream are not arranged next to each other at aboundary of two neighbouring frame intervals to avoid other negativeeffects of other negative (longer) fadings.

A schematic block diagram of a mapping apparatus 100 according to thepresent invention is shown in FIG. 8. The mapping apparatus 100comprises a data input 102, a data mapper 104, a mapping rule generator106, an embedding unit 108 and a data output 110. The data input 102receives n (at least two; in the embodiment of FIG. 7 four) mappinginput data streams (PLPs), S1, S2, . . . , Sn, which are each segmentedinto data blocks and carry error correction code encoded data for errorcorrection by the receiver. The received mapping input data streams S1,S2, . . . , Sn are forwarded to the data mapper 104 which maps the datablocks of said at least two mapping input data streams S1, S2, . . . ,Sn onto frames of a mapping output data stream according to an irregularmapping structure as explained above. In this embodiment the data mapper104 is provided with a mapping rule generated by a mapping rulegenerator 106. Said mapping rule generator 106 may, for instance,provide information to the data mapper 104 according to which sequencethe data blocks from the various mapping input data streams S1, S2, . .. , Sn shall be mapped subsequently onto the frame intervals of theframes of the mapping output data stream. After the mapping the datastream is provided from the data mapper 104 to the embedding unit 108 inwhich a mapping information is embedded into the mapping output datastream comprising an information about the applied mapping structure.For instance, the mapping information comprises the mapping rulegenerated by the mapping rule generator 106 and/or some parameters whichenable the receiver to reconstruct the applied mapping rule by anotherinstance of the mapping rule generator provided in the receiver. Themapping output data stream Q including the embedded mapping informationis then provided to the data output for outputting the mapping outputdata stream Q for further processing and transmission.

For illustrative purposes, a segment of such a mapping output datastream Q (before any subsequent processing) is shown in FIG. 9A in whichthe irregular mapping structure of the data blocks D1, D2, D3, D4 onthree subsequent frame intervals can be seen. In the transmitter (e.g.as shown in FIG. 1) the mapping output data stream Q is then furtherprocessed in various steps. For instance, in the OFDM Symbol Builder 37and the OFDM modulator 38 preamble symbols P1, P2 are added and the datastream is subjected to an IFFT processing. Therein, the repetitivecharacter and the sequence of the data blocks in the data stream iskept, but the OFDM symbols are generally formed such, that one OFDMsymbol does not necessarily comprise one data block, but—as shown inFIG. 9B depicting the mapping output data stream Q after suchpost-processing—one OFDM symbol O1, O2, O3, O4, . . . comprises onlypart of one data block D1, D2, D3, D4 or comprises parts from different(in the mapping output data stream Q subsequently arranged) data blocks.For instance, the OFDM symbol O1 comprises the first part of data blockD1 and the second OFDM symbol O2 comprises the second part of data blockD1 and the first part of data block D2.

A schematic block diagram of a corresponding de-mapping apparatus isshown in FIG. 10. The de-mapping apparatus 200 comprises a data input202, a de-embedding unit 204, a data de-mapper 206, a de-mapping rulegenerator 208 and a data output 210. The data input 202 receives atime-domain de-mapping input data stream Q′ which, after reception andpreprocessing by other elements of the receiver, generally correspondsto the mapping output data stream Q as outputted by the data output 110of the mapping apparatus 100. However, depending particularly on thecharacteristics and the quality of the transmission of the transmissionchannel more or less errors are included in the received de-mappinginput data stream Q′ compared to the mapping output data stream. Thede-mapping input data stream is then forwarded to the de-embedding unit204 which de-embeds any mapping information that had been embeddedtherein by the mapping apparatus as de-mapping information and forwardssaid de-embedded mapping information to the de-mapping rule generator208, whereas the de-mapping output data stream is forwarded to the datade-mapper 206. The de-mapping rule generator 208 reconstructs theinformation about the mapping structure according to which the datablocks from the various data streams are mapped onto the frame intervalsof the received de-mapping input data stream, in particular the mappingrule that had been applied by the data mapper 104. This de-mappinginformation is provided to the data de-mapper 206 which is then able tocorrectly de-map the data blocks from the de-mapping input data streamonto at least two de-mapping output data streams S1′, S2′, . . . , Sn′,which, if the de-mapping could be made correctly, correspond to themapping input data streams S1, S2, . . . , Sn provided as input to thedata mapper 104. These de-mapping output data streams S1′, S2′, . . . ,Sn′ are forwarded to the data output 210 from which they are outputtedfor further processing in the receiver.

By embedding the mapping information into the mapping output data streamas explained with reference to FIGS. 8 and 9 it is ensured that thereceiver knows sufficient information in order to correctly de-map areceived data stream. The additional signalling requirements for thisapproach, for instance compared to the current DVB-T2 specification, arevery limited. If the order of the data blocks is changed every frameinterval, the receiver is able to calculate the position within eachframe interval by means of the (generally known) length of each datablock and the known change of mapping structure.

However, other embodiments to ensure that the receiver can correctlyde-map a received data stream exist.

For instance, rather than embedding some information in the mappingoutput data stream by the transmitter, it is possible to use apredetermined and fixed mapping structure that is both known to thetransmitter and receiver in advance, e.g. because it is specified in astandard. Consequently the receiver does not need to receive anyinformation, for instance mapping information as mentioned above, alongwith the received data stream. In such a case the mapping rule generator106 and the embedding unit 108 as well as the de-mapping rule generator208 and the de-embedding unit 204 can be omitted in the transmitter andthe receiver, respectively according to one embodiment. In anotherembodiment, in this case, the mapping rule generator 106 and thede-mapping rule generator 208, but no embedding unit 108 and node-embedding unit 204 are provided in the transmitter and the receiver,respectively, since the mapping rule generator 106 and the de-mappingrule generator 208 are able to generate the mapping rule based on giveninformation about the predetermined and fixed mapping structure.

In a still further embodiment which does not require a rule generatorboth in the transmitter and the receiver, additional information may betransmitted along with a data stream that directly tells the receiverhow the data blocks have been mapped onto the frame intervals. Forinstance, a future extension frame (or parts thereof) of a superframe(see FIG. 4) could be used to insert sequence information that tells thedata de-mapper the sequence how the data blocks are arranged in theframes of the same superframe.

Similarly, in an embodiment such additional information allowing thereceiver to correctly de-map a received data stream can be inserted inthe header of each data block. For instance, some kind of addressinformation may be included in the header of each data block (asgenerally applied in DVB-H systems) telling the de-mapping apparatus towhich data stream the data block belongs.

If, as shown above in FIG. 7, the irregular mapping structure isobtained by changing the order of the data blocks from frame interval toframe interval, the mapping rule generator 106 (and also the de-mappingrule generator 208) may comprise a Linear Feedback Shift Register (LFSR)or any other Pseudo Binary Random Sequence (PRBS) generator. Similarpseudo random structures like e.g. demultiplexers, look-up tables orarchitectures as applied in the frequency interleaver according to theDVB-T2 standard, might be chosen, too. An embodiment of a practicalimplementation is illustrated in FIGS. 10 and 11.

FIG. 11 shows an embodiment of the frame comprising three subsliceintervals (frame intervals) and N physical layer pipes (mapping inputdata streams). To achieve a breaking of the regular mapping structurealong the time axis, as proposed according to the present invention, thedata block that starts within each frame interval is cyclically shiftedfrom frame interval to frame interval. This cyclic shift is reached bymeans of a shift factor. The starting positions of the individual datablocks within each frame interval can then be calculated by means of thelength of the data blocks within each frame interval (which are known tothe receiver anyway) and the shift factor. However, it is also possibleto apply other scrambling means, which may not keep the order of themapping input data streams from which data blocks are subsequentlyarranged within each frame interval.

FIG. 12 depicts an embodiment of an implementation for the generation ofthe shift factor. Its value is obtained by means of a linear feedbackshift register. At the beginning of each complete frame all registersare e.g. initialized with “1”. Then, the register is running freelyuntil the next complete frame, i.e. it is not re-initialized at thebeginning of the new frame interval, but at the beginning of a new framein this embodiment (in other embodiments the register may not bere-initialized at the beginning of each new frame that may thus continueto run freely). The “serial to N_(max) parallel” block takes N_(max)subsequent outputs of the register and creates a binary word consistingof N_(max) values. A factor N_(max) is the smallest possible number forwhich the equation N≦N_(max)=2^(K) with K=1, 2, 3, . . . holds. Here,the value N is the number of mapping input data streams.

The block “shift factor check” verifies that the resulting binary wordis smaller than the actual number of mapping input data streams, i.e.that the shift factor is smaller than N. If this equation is notfulfilled the shift factor is discarded and a new N_(max) binary word isgenerated by the register. If the shift factor is in the valid range, itis used within one frame interval to cyclically shift the data blocks asshown in FIG. 11. As mentioned above, a new shift factor is generatedaccording to this embodiment for each frame interval, and the registeris re-initialized at the beginning of each new frame.

Another embodiment by which an irregular mapping can be obtained shallbe illustrated with reference to FIG. 13 showing the absolute value ofthe channel transfer function superposed to one frame comprising threeframe intervals. According to this embodiment, the sequence of themapping input data streams from which data blocks are mapped onto theframe intervals is not changed from frame interval to frame interval,but the size of the data blocks is changed from frame interval to frameinterval (the frame intervals, however, have an identical fixed size).For instance, looking at the data blocks D1 it can be seen that in thefirst and second frame intervals F1, F2 they are rather short in time,while D1 is rather long in the third frame interval F3. Similarvariations are made to the other data blocks from other mapping inputdata streams. The effect is, as shown in FIG. 13, that the fades of thechannel transfer function do not affect only data blocks from the samemapping input data stream. For instance, in the first frame interval F1mainly data block D2 is affected, in the second frame interval F2 mainlydata block D3 is affected and in the third frame interval F3 mainly datablock D1 is affected. Thus, all data streams can be corrected by use ofthe error correction data in the receiver.

According to still a further embodiment the irregular mapping structurecan be obtained by a mix of a change in the sequence of the mappinginput data streams from which data blocks are mapped subsequently ontoframe intervals (as shown in FIG. 7) and changes in the sizes of thedata blocks (as shown in FIG. 13). In this case, however, moreinformation needs generally to be provided to the receiver to de-map areceived data stream.

In the above, embodiments have been described according to which, whenapplied to systems in accordance with or similar to the DVB-T2 standard,the mapping structure of data blocks mapped onto T2-frames is changed.According to another embodiment, the mapping structure of data blocksmapped onto T2-frames remains unchanged (e.g. as prescribed in theDVB-T2 standard), but only the mapping of data blocks mapped onto futureextension frames (FEF) is done irregularly in accordance with thepresent invention. Such an embodiment can, for instance, findapplication in data transmission systems in which the data transportedwithin the T2-frames is provided for reception by stationary receivers,while the data transported within the FEF frames is provided forreception by mobile receivers. Of course, in still another embodiment,it is also possible to employ the present invention for mapping of datablocks on both the T2-frames and the FEF frames.

The embodiments described above are, for instance, applicable to themapping of subslices (i.e. data blocks) of physical layer pipes (i.e.mapping input data streams) of type 2 as proposed in the DVB-T2standard. Such type 2 PLPs generally have two or more subslices (i.e.data blocks) per T2-frame, but the invention is also applicable if a PLP(or, more generally, a mapping input data stream) has only one subslice(i.e. one data block) per frame.

Further, the present invention may also be applied for the mapping ofsubslices (i.e. data blocks) of physical layer pipes (i.e. mapping inputdata streams) of type 1 as proposed in the DVB-T2 standard. Such type 1PLPs generally have only one slice per T2-frame, a slice being a set ofall cells of a PLP which are mapped to a particular T2-frame, i.e. insuch type 1 PLPs the slices are not further subdivided into subslices asis the case for type 2 PLPs. Such an embodiment shall be illustratedwith reference to FIG. 14 showing a simplified diagram of threesubsequent frames FR1, FR2, FR3, each comprising three PLPs (datastreams) S1, S2, S3 after the preambles P1, P2.

As can be seen that three PLPs (e.g. of type 1 in the sense of theDVB-T2 standard, i.e. which are not divided into subslices or datablocks) are mapped irregularly onto the subsequent frames FR1, FR2, FR3,i.e. the sequence of the three PLPs is changed from frame to frame. Thisgenerally provides the same advantage as described above that regularfadings or other regular disturbances do not only affect a single PLP toa large extent so that this PLP is much disturbed (e.g. so that it isnot (practically) reconstructable or correctable at the receiver), butdifferent PLPs are more or less equally affected to a much smallerextent.

An apparatus for mapping error correction code encoded time-domain dataof at least two, preferably a plurality of, mapping input data streamsonto a time-domain mapping output data stream having a frame structure,which is adapted for applying this embodiment, could then comprise adata input for receiving at least two mapping input data streamscarrying error correction code encoded data, a data mapper for mappingsaid at least two mapping input data streams onto frames of said mappingoutput data stream such that in each frame sequentially arranged variousmapping input data streams are sequentially arranged and that from frameto frame the mapping (in particular the sequence and/or the size) of thevarious mapping input data streams is different, and a data output foroutputting said mapping output data stream.

A corresponding apparatus for de-mapping a time-domain de-mapping inputdata stream having a frame structure into at least two de-mapping outputdata streams carrying error correction code encoded time-domain data,could then comprise a data input for receiving said time-domainde-mapping input data stream having a frame structure of frames, whereinin each frame sequentially arranged various de-mapping output datastreams are sequentially arranged and wherein from frame to frame themapping (in particular the sequence and/or the size) of the variousde-mapping output data streams is different, a data de-mapper forde-mapping the frames of said de-mapping input data stream into said atleast two de-mapping output data streams, wherein from frame to framethe de-mapping of said de-mapping input data stream into said at leasttwo de-mapping output data streams is made differently, and a dataoutput for outputting said at least two de-mapping output data streams.

It shall be noted that the above described variations and embodimentsare generally also applicable in the same or an equivalent manner onthis embodiment (as illustrated with reference to FIG. 14) of such anapparatus for mapping and an apparatus for de-mapping.

The proposed mapping and de-mapping according to the present inventionhelps to improve the performance of all communications or datatransmission systems that are affected by regular fades in timedirection. This is especially of importance for all kinds of mobilereceivers that suffer from Doppler frequencies causing exactly theseregular time fading effects. The proposed invention can be easilyadapted for use on the existing DVB-T2 architecture and could be apotential addition for other (existing or upcoming) DVB standards, suchas the upcoming DVB-NGH standard. However, the invention can generallyalso be applied to other digital mobile systems, like DAB or MediaFLO,which suffer from similar regular slicing or time interleaving. Testshave shown that the performance of such systems can be dramaticallydecreased by applying the suitable Doppler frequencies to the receiver,i.e. related receiver velocities, which problem could be overcome byapplication of the method as proposed by the present invention.

An embodiment illustrating the application of the present invention in aDAB system shall be explained with reference to FIGS. 15 and 16.

FIG. 15 shows the structure of a transmission frame as described in theDAB standard (ETS 300 401 “Radio broadcasting systems; Digital AudioBroadcasting (DAB) to mobile, portable and fixed receivers”, May 1997,RE/JPT-00DAB-4). The DAB transmission system combines three channels, inparticular a Synchronization Channel which is used internally with thetransmission system for basic demodulator functions (e.g. transmissionframe synchronization), a Fast Information Channel (FIC) which is usedfor rapid access of information by a receiver, which is anon-time-interleaved data channel and which can be sub-divided into FastInformation Blocks (FIBs), and a Main Service Channel (MSC) which isused to carry audio and data service component and which is atime-interleaved data channel divided into a number of sub-channels,which are individually convolutionally coded.

The MSC can also be seen as being made up of Common Interleaved Frames(CIFs), comprising Capacity Units (CU) as smallest addressable units.Each sub-channel of the MSC occupies an integral number of consecutiveCUs and is individually convolutionally encoded. More details regardingthe structure of the transmission frame and its content can be found inthe above cited DAB standards, which explanations are hereinincorporated by reference.

While, as shown in FIG. 15, the sub-channels SubCh a, SubCh b, . . . aresequentially arranged according to the standard, it is proposed in anembodiment of the present invention to change this regular structurefrom transmission frame to transmission frame as illustrated exemplarilyin FIG. 16. FIG. 16 shows three subsequent transmission frames Tr1, Tr2,Tr3 in which the sequence of the sub-channels has been changed fromframe to frame to avoid that regular fadings or other regulardisturbances affect the same sub-channel(s) in each transmission frame.

This kind of irregular mapping of the sub-channels on the transmissionframes can thus be used in a DAB transmission system, in particular in atransmitter and receiver of a DAB transmission system. For instance, themapping can be provided in a separate mapping apparatus or in the(already available) Main Service Multiplexer, Transmission FrameMultiplexer or FIC and MSC symbol generator. A mapping apparatus and acorresponding de-mapping apparatus can be adapted in the same way asdescribed above for the embodiment for DVB illustrated with reference toFIG. 14, wherein the sub-channels of the embodiment for DAB correspondto the physical layer pipes (generally the mapping input data streams)of this embodiment for DVB, and wherein the transmission frames of theembodiment for DAB correspond to the frames of this embodiment for DVB.

In the above, various embodiments for providing an irregular mappingstructure in the mapping output data stream have been described. Theseembodiments include variations of the sequence of mapping input datastreams, from which the data blocks are mapped onto the frame intervals,from frame interval to frame interval and/or variations of the sizes ofthe data blocks from frame interval to frame interval. These embodimentsfurther include variations of the sequence of data streams (e.g.physical layer pipes or sub-channels) within subsequent frames (e.g. DVBT2-frames or transmission frames). According to further embodiments itis possible to employ an irregular mapping structure by providingvariations in the size of data streams (e.g. physical layer pipes orsub-channels) within subsequent frames (e.g. DVB T2-frames ortransmission frames). Further, also the sizes of frame intervals and/orframes can be varied from frame interval to frame interval.

All the above described variations can be employed from frame intervalto frame interval and/or from frame to frame. But it is further alsopossible to employ such variations only after a number of frameintervals and/or frames. For instance, it is possible that in a firstgroup of frame intervals a first kind of (identical) variation isapplied, that in a second group of frame intervals a second kind of(identical) variation is applied, and so on. The same measure can beapplied to the variations of frames. Further, combinations of thosevariations are also possible.

The invention has been illustrated and described in detail in thedrawings and foregoing description, but such illustration anddescription are to be considered illustrative or exemplary and notrestrictive. The invention is not limited to the disclosed embodiments.Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. A single element or other unit may fulfill the functions ofseveral items recited in the claims. The mere fact that certain measuresare recited in mutually different dependent claims does not indicatethat a combination of these measured cannot be used to advantage.

A computer program may be stored/distributed on a suitable medium, suchas an optical storage medium or a solid-state medium supplied togetherwith or as part of other hardware, but may also be distributed in otherforms, such as via the Internet or other wired or wirelesstelecommunication systems.

Any reference signs in the claims should not be construed as limitingthe scope.

1. Apparatus (100) for mapping error correction code encoded time-domaindata of at least two mapping input data streams (S1, S2, . . . , Sn)onto a time-domain mapping output data stream (Q) having a framestructure, comprising: a data input (102) for receiving said at leasttwo mapping input data streams (S1, S2, . . . , Sn) each being segmentedinto data blocks (D1, D2, . . . , DN) carrying error correction codeencoded data, a data mapper (104) for mapping the data blocks (D1, D2, .. . , DN) of said at least two mapping input data streams (S1, S2, . . ., Sn) onto frames of said mapping output data stream (Q), each framecomprising a number of frame intervals (F1, F2, . . . , FM), wherein thedata mapper (104) is adapted for mapping the data blocks (D1, D2, . . ., DN) onto said frame intervals such that each frame interval (F1, F2, .. . , FM) carries sequentially arranged data blocks (D1, D2, . . . , DN)from various mapping input data streams (S1, S2, . . . , Sn) and thatwithin a frame the mapping of data blocks (D1, D2, . . . , DN) from thevarious mapping input data streams (S1, S2, . . . , Sn) onto frameintervals (F1, F2, . . . , FM) is different from frame interval to frameinterval, and a data output (110) for outputting said mapping outputdata stream (Q).
 2. Apparatus as claimed in claim 1, wherein the datamapper (104) is adapted for mapping the data blocks (D1, D2, . . . , DN)onto said frame intervals (F1, F2, . . . , FM) such that within a framethe sequence of mapping input data streams (S1, S2, . . . , Sn), fromwhich data blocks (D1, D2, . . . , DN) are mapped onto a frame interval,and/or the size of the data blocks (D1, D2, . . . , DN) arranged withina frame interval is different from frame interval to frame interval. 3.Apparatus as claimed in claim 2, wherein the data mapper (104) isadapted for mapping the data blocks (D1, D2, . . . , DN) onto said frameintervals (F1, F2, . . . , FM) such that within a frame the sequence ofmapping input data streams (S1, S2, . . . , Sn), from which data blocks(D1, D2, . . . , DN) are mapped onto a frame interval, and/or the sizeof the data blocks (D1, D2, . . . , DN) arranged within a frame intervalis different for all frame intervals (F1, F2, . . . , FM) of said frame.4. Apparatus as claimed in any preceding claim, wherein the data mapper(104) is adapted for mapping the data blocks (D1, D2, . . . , DN) ontosaid frame intervals (F1, F2, . . . , FM) such that the sequence ofmapping input data streams, from which data blocks (D1, D2, . . . , DN)are mapped onto the frame intervals (F1, F2, . . . , FM) of a frame,and/or the size of the data blocks (D1, D2, . . . , DN) arranged withina frame interval is identical for all frames.
 5. Apparatus as claimed inany preceding claim, wherein the data mapper (104) is adapted formapping the data blocks (D1, D2, . . . , DN) onto said frame intervals(F1, F2, . . . , FM) such that the sequence of mapping input datastreams (S1, S2, . . . , Sn), from which data blocks (D1, D2, . . . ,DN) are mapped onto the frame intervals (F1, F2, . . . , FM) of a frame,and/or the size of the data blocks (D1, D2, . . . , DN) arranged withina frame interval is different from frame to frame, in particular isdifferent for a plurality of subsequent frames or for all frames. 6.Apparatus as claimed in any preceding claim, wherein the data mapper(104) is adapted for mapping the data blocks (D1, D2, . . . , DN) ontosaid frame intervals (F1, F2, . . . , FM) such that within a frame eachframe interval comprises at least one data block (D1, D2, . . . , DN)from each mapping input data stream (S1, S2, . . . , Sn), in particularexactly one data block (D1, D2, . . . , DN) from each mapping input datastream (Si, S2, . . . , Sn).
 7. Apparatus as claimed in any precedingclaim, further comprising an embedding unit (108) for embedding amapping information into the mapping output data stream (Q) comprisingan information about the mapping structure of the mapping of the datablocks (D1, D2, . . . , DN) onto said frame intervals for enabling acorrect de-mapping of the mapping output data stream (Q).
 8. Apparatusas claimed in any preceding claim, further comprising a mapping rulegenerator (106) for generating a mapping rule for use by the data mapper(104) for mapping the data blocks (D1, D2, . . . , DN) onto said frameintervals according to said mapping rule.
 9. Apparatus as claimed inclaim 8, wherein the mapping rule generator (106) is adapted forgenerating said mapping rule comprising a sequence information for useby the data mapper (104) in determining the sequence of mapping inputdata streams (S1, S2, . . . , Sn), from which data blocks (D1, D2, . . ., DN) are mapped onto a frame interval, and/or a size information foruse by the data mapper in determining the size of the data blocks (D1,D2, . . . , DN) arranged within a frame interval.
 10. Apparatus asclaimed in claim 8 or 9, wherein the mapping rule generator (106)comprises a scrambling unit for generating a scrambling factor or ashift register, in particular a linear feedback shift register, forgenerating a shift factor for use as a sequence information by the datamapper (104) in determining the sequence of mapping input data streams(S1, S2, . . . , Sn), from which data blocks (D1, D2, . . . , DN) aremapped onto a frame interval.
 11. Apparatus as claimed in any precedingclaim, wherein the data input (102) is adapted for receiving said atleast two mapping input data streams (S1, S2, . . . , Sn) representingphysical layer pipes, each physical layer pipe being segmented intosubslices or bursts carrying error correction code encoded data. 12.Method for mapping error correction code encoded time-domain data of atleast two mapping input data streams (S1, S2, . . . , Sn) onto atime-domain mapping output data stream (Q) having a frame structure,comprising the steps of: receiving said at least two mapping input datastreams (S1, S2, . . . , Sn) each being segmented into data blocks (D1,D2, . . . , DN) carrying error correction code encoded data, mapping thedata blocks (D1, D2, . . . , DN) of said at least two mapping input datastreams (S1, S2, . . . , Sn) onto frames of said mapping output datastream (Q), each frame comprising a number of frame intervals (F1, F2, .. . , FM), wherein the data mapper (104) is adapted for mapping the datablocks (D1, D2, . . . , DN) onto said frame intervals such that eachframe interval (F1, F2, . . . , FM) carries sequentially arranged datablocks (D1, D2, . . . , DN) from various mapping input data streams (S1,S2, . . . , Sn) and that within a frame the mapping of data blocks (D1,D2, . . . , DN) from the various mapping input data streams (S1, S2, . .. , Sn) onto frame intervals (F1, F2, . . . , FM) is different fromframe interval to frame interval, and outputting said mapping outputdata stream (Q).
 13. Computer program comprising program code means forcausing a computer to carry out the steps of the method as claimed inclaim 12, when said computer program is carried out on a computer. 14.Transmission apparatus (20) for transmitting data within a datatransmission system, comprising: an apparatus (100) according to any oneof claims 1 to 11 for mapping error correction code encoded time-domaindata of at least two mapping input data streams (S1, S2, . . . , Sn)onto a time-domain mapping output data stream (Q) having a framestructure, and a transmitter unit (46) for transmitting said mappingoutput data stream (Q).
 15. Transmission method for transmitting datawithin a data transmission system, comprising the steps of: a methodaccording to claim 12 for mapping error correction code encodedtime-domain data of at least two mapping input data streams (S1, S2, . .. , Sn) onto a time-domain mapping output data stream (Q) having a framestructure, and a transmission step for transmitting said mapping outputdata stream (Q).